Dental caries and periodontal diseases are typical polymicrobial diseases, in which the pathogen(s) is also a member of the normal flora, which becomes pathogenic when the ecological balance of the commensal and pathogen is shifted toward overgrowth of the pathogen. Veillonella species, as an early colonizer and oral commensal, coaggregates with both commensal (S. gordonii, S. sanguinis, S. oralis, S. mitis etc) and pathogenic (S. mutans) streptococci during early stages of biofilm formation. Their utilization of lactic acid as a carbon source makes them an important player in balancing species composition in the dental biofilm. Indeed, epidemiological studies often find them associated with S. mutans in carious lesions however animal studies suggested that they may have a beneficial effect in terms of cariogenesis. Despite their prevalence in both supragingival and subgingival plaques and their implications in dental and periodontal health and disease, nearly nothing is known about the biology of these bacteria due to the lack of a genetic system. This study is the first attempt to develop a genetic system in the genus Veillonella. Two specific aims are proposed. Aim 1 is to test the transformability of Veillonella spp. PK1910 by using marker-bearing homologous DNA, and Aim 2 is to establish a protocol for transformation with foreign DNA, and to use this protocol to inactivate the type I restriction system that is deemed to be the barrier for tranformation with foreign DNA. A draft genome sequence of PK1910 is just completed in the PI's laboratory, and genomic analysis suggests that this bacterium may very well be transformable. If successful, this genetic system will contribute significantly to the understanding of this important yet least understood member of the oral biofilm community. PUBLIC HEALTH RELEVANCE: Dental caries and periodontal diseases are considered "polymicrobial diseases" whose etiology is an ecological shift in species composition of the dental plaque toward overgrowth of the pathogen. Veillonella species are prevalent in both supragingival and subgingival plaques and are implicated to play an important role in health and disease of the oral cavity. This study aims to develop a genetic system to better understand the biology and ecology of this important group of oral bacteria.